Electroactive Polymer Films Research Articles

Ellipsometry to Access Structural Information of Electroactive Polymer Films

Ellipsometry to Access Structural Information of Electroactive Polymer Films

Ions transfer mechanisms during the electrochemical oxidation of poly(3,4-ethylenedioxythiophene) in 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)amide ionic liquid

The cyclic voltammetry and the electrochemical impedance spectroscopy responses of p-doped poly(3,4-ethylenedioxythiophene) (PEDOT) electrodeposited on platinum electrode surface were studied in a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)amide (EMITFSI). The influence of adding salt, lithium bis((trifluoromethyl)sulfonyl)amide (LiTFSI, Li(CF 3SO 2) 2N), was studied. When PEDOT was prepared in acetonitrile, the cyclic voltammograms displayed two distinct anodic peaks indicating at least two redox reaction mechanisms. Results indicated that for one of these mechanisms 1-ethyl-3-methylimidazolium cation was the exchanged species during the oxidation, and at the same time bis((trifluoromethyl)sulfonyl)amide anion could be viewed as immobile ions trapped in the polymer film. The impedance responses were analyzed within two parallel diffusion paths that reflected the non-uniformity of the electroactive polymer film. The variation of the two time diffusion constants as a function of potential followed the same trend as the kinetic parameters determined by a potential step method. The total capacitance form electrochemical impedance spectroscopy was in agreement with that has obtained with cyclic voltammetry. Results showed also the importance of the electrodeposition conditions on the electrochemical behavior of PEDOT.

Electroactive Polymer Deformable Micromirrors (EAPDM) for Biomedical Optics

AbstractElectroactive polymers (EAPs) are capable of converting energy in the form of electric charge and voltage to mechanical force and movement and vice versa. Several electroactive polymer actuator materials whose responses are controlled by external electric fields, e.g. poly(vinylidene fluoride-trifluoroethylene) based fluoroterpolymers, have generated considerable interest for use in applications such as artificial muscles, sensors, parasitic energy capture, integrated bio-microelectromechanical systems (BioMEMS) and microfluidic devices due to their high electric-field induced strain, high elastic modulus, high electromechanical coupling and high frequency operation, etc. Scaling the EAP down into microsystems is one of the promising trends of EAP actuators and sensors especially for biomedical engineering. The combination of micro-optics and integrated BioMEMS, referred to as bio-micro-opto-electromechanical systems (BioMOEMS), makes a new opportunity for innovation in the EAP field. We present an approach to the fabrication of low-cost, large-stroke deformable micromirrors based on high performance electroactive polymer film microactuator arrays. Integrated Optic-BioMEMS based on electroactive polymer deformable micromirror (EAPDM) technology provide potential applications in biomedical optics such as ophthalmology (retinal imaging and vision care) and cancer detection and treatment.

Electropolymerisable bipyridine ruthenium(II) complexes: synthesis, spectroscopic and electrochemical characterisation of 4-((2-thienyl) ethenyl)- and 4,4 ′-di((2-thienyl) ethenyl)-2,2 ′-bipyridine ruthenium complexes

Four new ruthenium polypyridyl complexes with mono- or di-((2-thienyl) ethenyl) substituted bipyridines have been synthesized. The complexes were characterized by NMR, elemental analysis, UV–Vis absorption and electrochemistry (differential pulse and cyclic voltammetry). Electroactive polymer films of these complexes have been prepared by oxidative electropolymerisation and characterized by UV–Vis absorption spectroscopy and electrochemistry. The electrochemically induced polymerisation of the complexes resulted in a significant shift of the oxidation potential of the Ru(II)–Ru(III) process towards more positive potentials. Also, MLCT absorption band of the polymeric complexes is shifted towards shorter wavelengths. These results are interpreted in terms of an interruption of the conjugated system of the (2-thienyl)ethenyl-substituted bipyridine ligands due to a radical polymerisation mechanism affecting rather the ethenyl part of the ligand than the thienyl.

Thermally stimulated switching in electroactive polymer films

Electronic switching in poly(diphenylenephthalide) due to the thermal ionization of electron traps is studied. The method of thermally stimulated current and the method of thermally stimulated depolarization current are used. A correlation between spectra obtained by the two methods is established. The results are interpreted by using the temperature dependence of IR absorption spectra taken under conditions similar to those under which thermally stimulated phenomena are observed. Comparing data obtained, we assign electron traps to specific molecular groups of the polymer and infer the importance of the surplus space charge critical concentration for the onset of the high-conductivity state in the polymer.

Adsorption-Assisted Electro-oxidation of Dioxypyrrole and Dioxythiophene Monomers Probed by Fast Cyclic Voltammetry

The reactivity of the cation radicals formed by oxidation of four 3,4-alkylenedioxypyrrole and 3,4-alkylenedioxythiophene monomers has been investigated by fast scan cyclic voltammetry, from the V/s to the kV/s range. The results show that all cation radicals react quickly as desired for electropolymerization and electroactive polymer film formation on platinum and glassy carbon electrodes, despite the strong donating effect of the O-alkyl substituents. Surprisingly, the chemical reversibility of the cation radical formation and subsequent neutralization is easily observed on gold, due to a strong adsorption phenomenon, which greatly enhances the lifetime of the electrogenerated cation radical and reduces its formation potential. Surface coverage and electronic transfer coefficient measurements comparing the dioxypyrrole and dioxythiophene derivatives suggest a difference in how the adsorbed molecules orient relative to the electrode surface.

Quartz crystal microbalance: a useful tool for studying thin polymer films and complex biomolecular systems at the solution-surface interface.

The quartz crystal microbalance (QCM) is a simple, cost effective, high-resolution mass sensing technique, based upon the piezoelectric effect. As a methodology, the QCM evolved a solution measurement capability in largely analytical chemistry and electrochemistry applications due to its sensitive solution-surface interface measurement capability. The technique possesses a wide detection range. At the low mass end, it can detect monolayer surface coverage by small molecules or polymer films. At the upper end, it is capable of detecting much larger masses bound to the surface. These can be complex arrays of biopolymers and biomacromolecules, even whole cells. In addition, the QCM can provide information about the energy dissipating properties of the bound surface mass. Another important and unique feature of the technique is the ability to measure mass and energy dissipation properties of films while simultaneously carrying out electrochemistry on solution species or upon film systems bound to the upper electrode on the oscillating quartz crystal surface. These measurements can describe the course of electropolymerization of a film or can reveal ion or solute transport within a film during changes in the film environment or state, including the oxidation state for an electroactive film driven by the underlying surface potential. The past decade has witnessed an explosive growth in the application of the QCM technique to the study of a wide range of molecular systems at the solution-surface interface, in particular, biopolymer and biochemical systems. In this report, we start with a brief historical and technical overview. Then we discuss the application of the QCM technique to measurements involving micellar systems, self-assembling monolayers and their phase transition behavior, molecularly imprinted polymers, chemical sensors, films formed using the layer-by-layer assembly technique, and biopolymer films and point out the utility of the electrochemical capabilities of the technique to characterizing film properties, especially electroactive polymer films. We also describe the wide range of surface chemistries and attachment strategies used by investigators to bring about surface attachment and multi-layer interactions of these thin film systems. Next we review the wide range of recent applications of the technique to: studies of complex biochemical and biomimetic systems, the creation of protein and nucleic acid biosensors, studies of attached living cells and whole cell biosensor applications. Finally, we discuss future technical directions and applications of the QCM technique to areas such as drug discovery.

First conducting polymer functionalized with covalently linked carborane units

The anodic oxidation of a carborane-substituted pyrrole leads to the formation of an electroactive polymer film ( σ∼10 −1 S cm −1) which shows a strongly increased overoxidation resistance in comparison with unsubstituted polypyrrole.

Use of the Flux Ratio Method for Mechanistic Diagnosis in Electroactive Polymer Film Redox Switching

The redox switching of poly(vinylferrocene) (PVF) films was investigated using the electrochemical quartz crystal microbalance in conjunction with cyclic voltammetry (at different voltage scan rates) and reverse potential steps. The mechanism of the redox process was determined using PVF films supported on Au electrodes and exposed to aqueous bathing solutions of 0.1 M sodium hexafluorophosphate. PVF electro-oxidation proceeds via coupled oxidation of uncharged ferrocene sites and entry of counterion and is followed by the entry of water into the film. Structural changes within the polymer may also accompany the latter two steps. Any of these three steps may be the slowest for particular redox conditions. The controlling kinetic step depends on the film’s instantaneous water content, its instantaneous oxidation state, the electrochemical control function, the direction of redox switching, and the associated time scale of the experiment. We describe a new general quantitative approach based upon comparison of the instantaneous fluxes of solvent (water) and counterion during the redox cycle to characterize the rate-controlling process as a function of the extent of film oxidation. This new methodology has the capability to resolve time scale- and potential- (charge-) dependent mechanistic shifts and film relaxation phenomena as they are reflected through the ratio of fluxes of solvent and counterions. © 2003 The Electrochemical Society. All rights reserved.

Electroactive polymer films for stainless steel corrosion protection

Electroactive polymer films of polyaniline, poly-o-toluidine and a composite of both were deposited on stainless steel and their performance as protective coatings against corrosion was evaluated. Open circuit potential and potentiodynamic studies of the polymer-coated stainless steel in a corrosive medium showed a significant shift in the corrosion potential towards more positive values. Mechanical characteristics of the films were evaluated by means of microhardness measurements, revealing nonelastic films in all cases and low hardness values that increased from polyaniline to poly-o-toluidine to the composite. The best results were obtained in the case of the polyaniline-o-toluidine composite.

Electrochemical properties and Fourier transform-infrared spectroscopic investigations of the redox behaviour of poly(indole-5-carboxylic acid) in LiClO 4-acetonitrile solutions

Electropolymerisation of indole-5-carboxylic-acid leads to the formation of electroactive polymer films. Potentiostatic deposition of the related polymer, poly(indole-5-carboxylic-acid), was carried out at a constant potential at 1.35 V versus SCE. The cyclic voltammogram of the resulting polymer in LiClO 4 (0.15 mol dm −3)/acetonitrile solution is characterized by two poorly resolved anodic and cathodic set peaks. FTIR spectroscopy was used to characterize both reduced and oxidized forms of poly(indole-5-carboxylic-acid). Assignments of the vibrational modes were proposed by comparison of the vibrational spectra of polyindole and polycyanoindole. The polymerization sites correspond to the 2 and 3 carbon positions of the pyrrole cycle. In the oxidized form of the polymer, the NH group is deprotonated while the quinoı̈d form is present between the pyrrole rings.

Conducting Polymers as Coatings: Electrochemical and density functional theory investigations of the polymerisation of (Z)-α,β-2-diarylacrylonitriles

SUMMARYElectroactive materials such as polypyrrole and polythiophene have many applications including their use as coatings in the metal finishing industry. Electrochemical and density functional theory (DFT) studies of a series of derivatised thiophene molecules have revealed that the production of electroactive polymeric films can be related to the coupling pathways of the radical cations generated during anodic oxidation of the monomer. Electro-oxidation of (E)-styrylheterocycles shows complex electrochemical behaviour with alkene oxidation preceeding that of the aromatic/heterocyclic rings to produce redox inactive insulating films. A nitrile Substitutent was introduced at the alkene spacer linkage in an attempt to alter the electron density distribution in the radical cation and thus minimise the likelihood of adverse couplings via this site. This strategy proved successful with redox-active polymers formed on oxidation of (Z)-αc,β-diarylacrylonitriles. Viese results were supported by the use of DFT which confirmed that the π-spin density at the alkene spacer linkage was significantly reduced in the presence of the nitrile substituent allowing α,α’-coupling reactions to predominate.

Effect of thermal treatment on dielectric and acoustic properties of P(VDF/TRFE) film

Electroactive polymer films are widely applied in electroacoustic transducers and their properties can be tuned by matching the conditions of thermal treatment to the requirements of various devices. As the dielectric properties determine the piezoelectric response of the film we studied the effect of annealing at various temperatures on the dielectric dispersion of P(VDF/TrFE)(75/25) copolymer film. The most effective thermal treatment (in TC range) results in an increase in dielectric permittivity value and shifts the β-relaxation and piezoelectric resonance towards higher frequencies. The effect is related to the reduction of compensating charges piled up at the crystalline phase of the semicrystalline polymer. The heterogeneity of P(VDF/TrFE)(75/25) film annealed at temperatures in the TC range is also reflected in a complex acoustic response studied in one-side clamped conditions. Moreover, the room temperature sound velocity of the annealed copolymer film is considerably higher than that of non-annealed film.

Workshop on Electrochemistry of Electroactive Polymer Films

Workshop on Electrochemistry of Electroactive Polymer Films

Electropolymerisable bipyridine ruthenium(II) complexes. Synthesis and electrochemical characterisation of 4-(3-methoxystyryl)- and 4,4′-di(3-methoxystyryl)-2,2′-bipyridine ruthenium complexes

A number of new ruthenium polypyridyl complexes with mono- or di-(3-methoxystyryl) substituted bipyridines have been synthesized. The complexes were characterised by NMR, elemental analysis, UV-vis absorption and emission spectroscopy, and cyclic voltammetry. Electroactive polymer films of these complexes have been prepared both by oxidative and reductive electropolymerisation. The polymers have been characterised by UV-vis absorption spectroscopy and cyclic voltammetry. Possible processes involved in the polymerisation and the structure of the film are discussed.

In situ neutron reflectivity studies of poly-o-toluidine films

Our long-term scientific objective is the rational design and fabrication of electrochemical interfaces of specific function, via modification of the electrode with thin films of electroactive polymers. This requires us to understand the relationship between electrode performance and structure. From a series of experiments performed on the TAS8 reflectometer at Risø National Labs, we have studied the spatial distributions of polymer and solvent within poly(o-toluidine)(PoT) films in their reduced form, as functions of film thickness and pH in perchloric acid solutions. We intend to use our in-situ neutron reflectivity data to rationalize electrochemical quartz crystal microbalance (EQCM) and probe beam deflection (PBD) data on redox driven PoT ion and solvent transfer dynamics.

Electroactive Polymer Films Formed from the Schiff Base Product of 1,8-Diaminonaphthalene and Dehydroacetic Acid. I. Preparation and Characterization

We report on the preliminary synthesis and characterization of an electroactive, conducting polymer that should readily bind metal cation. Anodic polymerization of the Schiff base resulting from the condensation reaction between 1,8‐diaminonaphthalene and dehydroacetic acid, 8‐(3‐acetylimino‐6‐methyl‐2,4‐dioxopyran)‐1‐aminonaphthalene, on platinum electrode in acetonitrile was found to yield thin, electroactive polymeric films. The films were found electroactive in acetonitrile and aqueous sulfuric acid solution and the electroacity is attributed to the electron transformation of the amino/imine sites in the polymer as in aromatic amine polymers. Electrochemical studies of electron‐transfer reactions on the polymer‐covered platinum electrodes indicated that the polymer films are highly porous and semiconducting. © 2000 The Electrochemical Society. All rights reserved.

Photolithographically-Patterned Electroactive Films and Electrochemically Modulated Diffraction Gratings

This manuscript presents an overview of work directed toward the creation of arbitrary micron-scale patterns of electroactive polymer films by the application of photolithography. A brief overview of work by other groups in the field is followed by a detailed description of work from our own labs which resulted in the development of methods to pattern a variety of different electroactive materials, including Ru− and Os−polypyridine complexes, viologen-based polymers, and a low-potential polythiophene. The discussion provides detail on the photolithographic methodology. In addition, the spatially-patterned films are characterized by using optical and scanning electron microscopy. The voltammetric and spectroelectrochemical properties of several of the lithographically-patterned films are also presented. Finally, photolithography is applied to fabricate electrochromic optical diffraction gratings. The diffraction efficiency of these electroactive gratings can be modulated by an electrochemical stimulus. The properties and mechanism for operation of the electrochromic gratings are described.

Study of charge transport processes in Prussian-blue film modified electrodes

Charge transfer processes within Prussian-blue (PB) films were studied by using different non-stationary methods, namely cyclic voltammetry, chronopotentiometry and chronoamperometry, at different film thickness, different type and concentrations of adjacent electrolytes (0.1–1 M KCl with pH 2–4). As a result of the above measurements the electro-diffusion mechanism of the processes was revealed. Using a low amplitude variant of chronoamperometry in the range of electrode potentials from 0.1 to 0.3 V, we established that, within the main time interval of the measurements, the current decay satisfies the well-known Cottrell equation. The interpretation of current transients was based on model representations of charge transfer processes in electroactive polymer films. The latter were modeled as a binary electrolyte whose immobile components are the redox centers participating in an electron exchange reaction in the film interior. At the same time, cations absorbed by the film from the adjacent solution were considered as mobile charge carriers in such films. Theoretical inferences for the current response at low amplitude perturbations in the electrode potential were obtained for this model. The theoretical conclusions are in good agreement with the obtained experimental data. As a result of the analysis performed, a limiting character of ionic transfer processes in PB films was established.

Polyterthiophene appended by transition-metal cluster: electropolymerization of 3′-[CCo 3(CO) 9]-5,2′:5′,2″-terthiophene

Terthiophene, to which cobalt carbonyl cluster complex is π-conjugated, 3′-[CCo 3(CO) 9]-5,2′:5′,2″-terthiophene (3′-CoTTh), was prepared by reaction of 3′-chloromercuro-5,2′:5′,2″-terthiophene with HCCo 3(CO) 9. The molecular structure of 3′-CoTTh is identified by spectroscopic methods and elemental analysis. Cyclic voltammetry of 3′-CoTTh showed deposition of electroactive polymer films on the electrode surface. The absorption spectra of 3′-CoTTh and its polymer films are presented.